Could be either/or. I long ago lost the brassiere that came with my AirPods Max (not really lost, I just can’t be arsed to dig it out of where I think it is) and they’ll drain themselves fairly quickly just trying to throw out stray connections to any of the five or so devices they can connect to unless I make a point of disconnecting them. AirPods Pro exhibit the same exact symptoms when the contact inside the case needs to be cleaned.

If Person A loses 1% over a week in standby, and person B loses 20% overnight, it's probably not the battery..

Unless Person B also tells you that in general their air pods only last 30 minutes playing music.

As stated, their percentage of power level fall vs person A is 2000% more being generous (person A said a week, not a night). If it was because of the battery, the air pods would also last way way way less playing music.